Electric fuse



Nov. 1s, 1943.

F. S. KLE

ELECTRIC FUSE Filed Jan. 6,

INVENTOR.

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Patented Nov. 18, 1941 UNITED STATES PATENT OFFICE ELECTRIC FUSE Franklin S. Klein, Malverne, N. Y.

Application January 6, 1941, Serial N o. 373,499

11 Claims.

This invention relates to electric fuses and particularly to fuses of the type known as nontamperable plug fuses; and the invention includes what is known as an adapter for a nontamperable plug fuse.

An object of this invention is to provide a plug fuse and an adapter having more of a nontamperable character than prior plug fuses and adapters; and this object is attained by providing a plug fuse with a suitable cavity in the bottom center thereof and a contact member having a contact surface exposed within that cavity, whereby, the fuse may function in a fuse receptacle provided with a suitable bottom center terminal, preferably an adapter, which will electrically connect the fuse only by entering said cavity.

Another object is to provide a plug fuse which is nontamperable when used with a suitable adapter, and also adapted for ordinary use without an adapter. Another object is to provide a nontamperable plug fuse which will cost no more than ordinary plug fuses. All of these objects may be attained at once by means which include a plug fuse of standard type having a bottom center contact whereby the fuse can function as usual, and having that bottom contact provided with a smooth round cavity whereby the fuse may also function in a fuse receptacle provided with a nontamperable or selective bottom. terminal adapted to electrically connect the bottom contact of the fuse only by entering said cavity.

With these objects attained, I eliminate the inconvenience of stocking plug fuses of different types having the same electrical characteristics, and also eliminate the usual extra cost of nontamperable plug fuses. v

A further object of this invention is to provide a fuse adapter having more of a nontamperable character than prior fuse adapters which are provided with an opening through which an electrical connection is made by means of direct pressure on a pin or contact in line with the axis of the fuse and receptacle; in such prior adapters foreign material may be used in said opening. Therefore, another feature of this invention is an adapter having a contact member which can be moved into the electrical circuit only by lateral pressure and only by means of a fuse having a special contact at the bottom thereof.

Other novel features which simplify the manipulation, increase the selective qualities, and nontamperability of this new fuse are hereinafter set forth; and it will be noted. that I have provided athoroughly nontamperablefuse device by combining with the present invention the nontamperable feature set forth in my pending applications for: Electric fuse, No. 206,743 filed May 6, 1938, and No. 273,882 filed May l5, 1939.

In the drawing Fig. 1 is a sectional elevation through a fuse receptacle, and a fuse plug, and an adapter, embodying the present invention. Fig. 2` is a view of the bottom of the fuse plug at Fig. 1. Fig. 3 is a view of the unassembled parts of the adapter at Fig. 1. Fig. 4 is a sectional elevation through a modification of the invention at Fig. l. Figs. 5 and 6 are detailed sectional views of parts of the adapter and the cooperating plug fuse, shown in Figs. 1 and 4 respectively.

Fig. 1 includes a standard plug fuse receptacle, and the number I indicates the receptacles nonconducting casing, 2 is the screw threaded terminal shell, 3 is the bottom center terminal having a -substantially flat contact surface, 4 and 4 are extensions of the terminals 2 and 3 and provided with screws 5 and 5 to connect the receptacle in the electric circuit.

Fig. 1 includes a plug fuse of standard type, having a nonconducting casing at 6, and provided with a fuse chamber at 'I, 8 is the top closure of the fuse chamber and includes transparent material 9 through which to view any thermally operated device in the casing where a fusible element in the preferred form of a fuse link at I0 is shown to be connected to the usual contact shell Il which is screw threaded to correspond with the fuse receptacle, and also connected to a contact I2 which has a contact surface at the bottom surface of the fuse.

I have just described a fuse of standard type, but, by providing the bottom contact I2 with a conical cavity or cam recess as at I3, I have made the fuse also useful in selective receptacles which are provided with a bottom contact adapted to electrically connect with the fusible element I0 only by entering the cavity I3. Furthermore, the proportions of the cavity I3 are to be understood as being related to the electrical characteristics of the fusible element at I0, and, as fusible elements vary, so will the proportions of this cavity vary to prevent the fuse from functioning in combination with a fuse receptacle adapted for fuses of lower capacity.

Also at Fig. l is shown a new adapter which comprises a body of insulation I4 in the form of a relatively shallow plug having an external screw thread I5 which corresponds with the receptacles threaded terminal shell. This body of insulation is provided with a contact chamber at I6, and on the bottom center of the adapter is a contact I'I which extends into said chamber through spaced small slots at I8 and I8 to form spaced contact terminals at I9and I9.

At 20 and 20 are twin contact members having their lower portions in the chamber l`6 and their upper portions extending above the top center of the adapter through an aperture 2| in the top of the body of insulation; 22 is a resilient means in the preferred form of a spring which is clearly shown at Fig. 5 and will be described.

This spring is arranged to constantly urge the twin members together and away from the spaced terminals I9 and I9 in the chamber; and if the adapter is not in use, this spring holds the upper portions of the twin contact members apart and in position to closely enter the opening ofA the conical cavity I3 and be squeezed together by the conical cam walls thereof as shown, causing the lower portions of the twin members to spread and connect with the spaced terminals I9, I9, in thechamber I6.

The upper portions of the twin members 20, ZIJ, are, when squeezed together, proportioned to conform closely with the proportions of the conical cavity I3 in the fuse, and will function only with a fuse having the proper cavity. vTherefore, these twin members are also proportioned with relation to the electrical characteristics of the fusible element at I to prevent the use of a fuse that may permit the circuit to be overloaded.

At Fig. 3which shows the unassembled parts of the adapter shown in Fig. 1, I4 is insulating material and the main body of the adapter which includes a top section 23 and a bottom section 24 secured together preferably by means of rivets 25 and 25 through holes at 26 and 25, and provided with a contact chamber I6. The top section 23 being provided with an aperture 2l, through which the twin contact members 20,- 20 are closely fitted to prevent tampering, yet this aperture permits the necessary movement of these twin members which extend out of and above the body of insulation.

At I1 is the external bottom contact member of the adapter, formed from a single piece of flat resilient metal which has been first bent into a rectangular U shape, then having each end of the U bent sharply outwardly and down to form two inverted Vs which provide resilient spaced terminals I9, I9, in the contact chamber. When made as shown, these spaced terminals are easily squeezed through the narrow Yspaced slots I8, I8, in the bottom of the adapter, whereupon, the terminals I9, I9, return to the shape of inverted Vs and safely secure the Contact member I`1 to the bottom of the adapter.

At Fig. 3, the spring 22 is shown to be somewhat in the form of a letter Z and preferably formed from flat material; 21 and 21 are two recesses in the side walls of the chamber I6 to receive the angular points 28 and 28 of the spring and hold it in position in the adapter; 20 and 20 are the movable twin contact members, each having a notch 29 in its outer side to engage the free ends 38 and 30 of the Z shaped spring whereby, these twin members are retained in the adapter and their lower portions constantly urged together and from the spaced terminals I9, I9, in the chamber; consequently, the midmember 3l of this Z shaped spring happens between the twin members and serves to hold them at the exact center of the adapter; and a small ridge or abutment 41 on the bottom of the chamber I6, helps to steady the twin members.

The upper portions of the twin members extend above the main body of the adapter and are so formed as to be spaced as at 32 when not engaged with a fuse, and proportioned for close admission into the opening of the conical cavity I3, whereby, gradual engagement of these twin members with the side walls if the conical cavity permits their upper portions to be moved laterally or squeezed together and electrically connected to both the side walls and back or top wall of the cavitied bottom contact of the fuse, while the lower portions of these members spread apart and electrically connect with the spaced terminals I9, I9 in the chamber as shown at Fig. l.

Further at Fig. 3, 33 and 33 are irregular recesses provided in the top of bottom section 24 of the adapter to receive irregular spaced pieces of spring wire 34 and 34, one of which is shown in position; and with the top section 23 of the adapter riveted in position, these springs are held in position with their ends 48 and 48 projecting tangentally from the external thread of the adapter to form short spurs which lock or hold the adapter irremovable in the receptacle by digging into the terminal shell l2 if an attempt is made to remove the adapter.

Another feature of this invention is the arrangement at the bottom of the plug fuse and at the top of the adapter of complementary formations which are adapted to releasably engage, whereby, the fuse constitutes a toolsuch as a key or wrench for screwing the adapter into position in the threaded receptacle shell.

'These complementary formations comprise a series of corrugations at 35 arranged annularly in the bottom of the plug fuse and a corresponding arrangement of corrugations 36 on the top of the adapter. The corrugations 35 are preferablyy in an annular recess 31 ink the bottom of the fuse casing as at Figs. 1 and 2|, and the cooperating corrugations 36 are ona rib 38 projecting from the top of the adapter as at Figs. 1 and 3.

This corrugated rib and recess cooperate to guide the center contacts of the adapter and plug fuse into engagement, and also prevent the use of conductive material other than a fuse for which the receptacle has been adapted, for, material such as a coin would prevent the necessary lateral pressure on the twin contact members, and material such as tin foil which may conformy with the recess 31 and rib 38 would be torn or dislodged bythe engagement of the corrugations 35 and 36.

It must be obvious that the adapter set forth at Fig. 1, `would function if only one of the twin members 20 were present and extending through a suitable aperture at 2|, or, if one of these twin members were stationary, or, if one of these twin members were of nonconducting material.

However, Fig. 4 shows a modication of the invention which includes an adapter having a single movable contact member at 39 to operate with lateral pressure counter to the pressure of the. spring 22 which needs but one free end 30 to engage the notch 279 in this single movabletcontact member.V

At Fig. i the plug fuse has a bottom contact at 4I provided with a cylindrical cavity at40 extending into the bottom center of thebody of the fuse instead of a conical cavity as at Fig. 1. In this instance the nonconducting casing 6 forms the side wall-of the cavity andthe bottom contact 4| has a surface exposed only at the back or top wall of the cavity. This fuse has even more of a nontamperable character than the fuse at Fig. 1, and may be frequently preferred for that reason, or because it is not adapted for more general use. However, it must be obvious that a contact as at 4| may have cylindrical walls which extend to the bottom surface of the fuse casing and thereby also serve for general use like the fuse at Fig. 1, or, the cavity in the fuse at Fig. 4, may be conical and function with the adapter at Fig. 1.

At Fig- 4 the upper part of the movable contact member 39 has the contour of a wedge with at least one side curved as at 42. Then, when the fuse is not engaged, the spring 22 urges each end of the member 39 in opposite directions for about twenty degrees off from the axis of the fuse and adapter, whereby, the upper part of member 39 constitutes a cam which receives motion by having the curved side 42 bearing and sliding against the edge of the opening of the cylindrical cavity as the fuse and adapter engage, thus moving the member 39 until its lower portion connects with the terminal I9 in the chamber of the adapter and its upper portion connects with the bottom contact 4l in the cavity of the fuse.

At Fig. 4 the recess 43 with corrugations 35 in the bottom of the fuse casing, and the rib 44 with corrugations 36 at the top of the adapter, serve the same purposes as the corrugated rib and recess at Fig. l, but are shown to be triangular in cross-section and illustrate an example of interfitting formational limitations, which may also be dimensional as well, for preventing the use of any but the proper fuse with a particular adapter. Limitations of the same character may also be used in forming the cavity in the bottom of the plug fuse and the corresponding movable contacts of the adapters, then a contact member as at 20 in Fig. 1, or, at 39 in Fig. 4, will not enter a cavity that is too small, nor be sufficiently moved when the cavity is too large.

The plug fuses at Figs. 1 and 4 include a nontamperable feature set forth in the prior applications mentioned above. That feature, in a plug fuse, comprises a mass of nonconducting solid material in which a portion of the potentially fusible section of a fuse link is embedded and protected to prevent tampering with the current carrying value of the fuse, before r after a, rupture of the fuse link. At Figs. 1 and 4, this feature is shown as a fuse link at I0, having a potentially fusible longitudinal section at 45 partly embedded in a body of porcelaineous cement at 46.

This new fuse device is operated by first entering the adapter in the threaded shell of the receptacle by means of the fingers, then by pressing the fuse against the adapter, the recess in the bottom of the fuse and the rib at the top of the adapter mesh and guide into electrical connection the surface of the contact in the cavity of the fuse and the movable contact member of the adapter, and also guide the cooperating corrugations into engagement. At this point it may be necessary to operate the plug fuse in ratchet fashion until the threads of both fuse and adapter coordinate with the thread of the receptacle shell in order to screw the adapter to the bottom of the receptacle, whereupon, the electric circuit through the receptacle will be complete.

I claim:

l. A non-tamperable fuse device comprising,

in combination, a fuse receptacle; a fuse adapter comprising an insulating body having a chamber, an external contact terminal extending into said chamber, a contact member having a lower portion movable laterally within the chamber into contact with said contact terminal and an upper portion extending through the top of the insulating body, resilient means urging the lower portion of the contact member away from the contact terminal; and a plug fuse having a contact member exposed at its bottom and formed to engage the upper portion of said movable contact member and to move ysaid movable contact member to cause its lower end to move laterally into electrical contact with the external contact terminal.

2. A non-tamperable fuse device, as deiined in claim 16, wherein the fuse adapter and plug fuse are similarly threaded and formed for interlocking interengagement for introduction of the adapter and plug fuse together into the fuse receptacle, said adapter having means cooperating with the fuse receptacle to inhibit reverse movement whereby the adapter will remain in place in the fuse receptacle when the plug fuse is removed.

3. A non-tamperable fuse device comprising, in combination, a fuse receptacle; a fuse adapter comprising an insulating body provided with a chamber, an external contact terminal extending into said chamber, a contact member having a lower portion movable laterally within the cham.- ber into contact with said contact terminal and an upper portion extending through the top of the insulating body, resilient means urging the lower portion of the contact member away from the contact terminal; and a plug fuse having a central cam recess at the bottom center thereof in position to engage the upper portion of said movable contact member and to move said movable contact member to cause its lower end to move laterally into electrical contact with `the external contact terminal, and having a contact element exposed at the bottom face thereof and at the cam recess to make electrical contact with said movable contact member.

4. An adapter for a plug fuse and plug fuse receptacle, comprising a body of insulation fitted for insulation with the plug fuse into the plug fuse respectively provided with a chamber and a terminal attached to the bottom of said body of insulation and extending into the chamber; a movable contact member having a lower laterally movable portion thereof in said chamber and an upper portion extending through an aperture provided in the top of said body of insulation, resilient means constantly urging said lower portion of the movable member laterally from said terminal in the chamber, and all so arranged that lateral movement of said upper portion of the movable member may move the lower portion thereof into contact with said terminal in the chamber.

5. An adapter for a plug fuse and a plug fuse receptacle, comprisingy a body of insulation provided with a chamber and having a contact at the bottom extending into the chamber; twin movable contact members having lower portions thereof in said chamber and upper portions extending through an aperture provided in the top of said body of insulation, spring means urging said twin members from said contact in the chamber, all being arranged for lateral movement of said upper portions of the .twin members to move the lower portions thereof into connection with said bottom contact of the adapter.

6. An adapter .for plug fuses andplug fuse re` ceptacles, comprising a body of insulation provided with a contact chamber and a contact at the bottom of said body; spaced contact terminals in said chamber and connected with said contact at the bottom vof said body, movable twin contact members having lower portions thereof in said chamber and upper portions of the members spaced and extending above 'said body through an aperture provided in the top thereof, and a spring in said chamber urging said lower portions of the twin members together and from said spaced terminals in the chamber, whereby, a suitable plug fuse may move said upper portions'of the twin members toward each other and thereby spread lsaid lower portions into connection with said spaced terminals in the chamber.

7. A nontamperable fuse device comprising, in combination, a fuse receptacle; a fuse adapter comprising a body yof insulation provided with a chamber, an external contact terminal extending into said chamber, a laterally movable contact member having a lower portion in said chamber and an upper portion of the member extending through an aperture provided in the to-p of said body of insulation, and resilient means urging said lower portion of the movable member from said terminal in the chamber; and a plug fuse provided with a cavity at the bottom center thereof, and a contact member having a smooth contact surface exposed within said cavity, the fuse being adapted to engage the upper portion of said movable member in said cavity and thereby move the movable contact member laterally into electrical connection with said contact of the fuse and said terminal in the chamber.

8,. A nontamperable fuse device as dened in claim 7, wherein, said plug fuse comprises a fuse link having a portion of a potentially fusible section thereof embedded and protected in a body of solid nonconducting material and therewith forming a tamper proof mass, to prevent tampering with the current carrying value of the fuse link. l 1

9. A nontamperable fuse device-comprising, in combination; a plug fuse receptacle; a fuse adapter comprising a body of insulation provided with a Contact chamber, spaced contact terminals in said chamber connected with a contact on thebottom'of the adapter, laterally movabl'e'twin contact members having lowerportions thereof in said chamber and upper portions thereof extending above said body of insulation through an apertureprovided in the top thereof,

said twin members being adapted to be moved laterally together'at lthe upper portions `thereof and thereby spread the lower portions ofthe members into connection with said spaced terminals in the chamber, and resilient means constantly urging saidlower :portions of the twin members from said spaced terminals; and a plug fuse having a contact with an exposed surface within a conical cavity provided at the bottom of the fuse, and thereby adapted to move saidtwin terminals into electrical connection with said contact of the fuse and said spaced terminals, in the chamber. f

l0. A nontamperable fuse device comprising, in combination, a fuse receptacle having a screw threaded terminal shell and a bottom center terminal; a fuse adapter comprising a relatively shallow plug of insulation having a screw thread to correspond with said terminal shell and prof vided with a contact chamber, an annular rib provided with corrugations at the 'top of said plug` of insulation, spaced vcontact terminals in said chamber connected with a contact on the bottom center of the adapter, laterally movable twin Contact members having their lower portions in said chamber and their upper portions spaced and extending above said insulation through an aperture in the top thereof, a spring constantly urging said twin members together and from said spaced terminals in the chamber; anda plug' fuse comprising a casing, a contact shell screw threaded to correspond with said shell terminal, a contact at the bottom of the fuse provided with a conical cavity, said cavity being proportioned with relation to the fusible element of said fuse and adapted to closely admit said upper portions of the twin members andmove them laterally together and thereby spread said lower portions of the twin members into connection with said spaced terminals in the chamber, said casing being provided with an annular recess with corrugations therein to engage said corrugated rib at the top of the adapter whereby, the yfuse may be used vto screw the adapter into the receptacle; said fuse'being adapted for use in said receptacle without an adapter.

ll. A nontamperable fuse device as 'defined in claim 10 wherein, said plug fuse comprises, a fuse link having a potentially fusible longitudinal section, and a solid nonconductingmass in which a portion of said potentially fusible section is embeddedr and protected to prevent tampering with the current carrying value of the fuse link.

FRANKLIN S.r KLEIN. 

